外轮廓边界搜索参数对放疗靶区和危及器官的剂量学影响

目的:对比双面膜固定条件下，外轮廓自动搜索参数设置引入的体积差异对靶区和危及器官的剂量学影响。方法:选取25例双面膜固定的全脑放疗患者，保持其他搜索条件不变的前提下，改变外轮廓搜索条件（平滑度、CT值阈值和后处理方法）并重新进行剂量计算，共计9种方案。对比改变参数后的计划与默认设置计划（Default）靶区和危及器官的剂量差异。结果:搜索条件中的平滑度和CT值对外轮廓和靶区的剂量指标影响较大。在DSL0、DSL1、DSL2、HU-550和HU-750计划中，靶区的Dmean和外轮廓的Dmax变化较明显；外轮廓Dmean的变化均值在HU-750计划中超过400 cGy。结论:Eclipse计划系统默认的搜索外轮廓的方式不适合所有情况，低平滑度和低HU限值条件搜索的外轮廓对剂量影响较大。针对全脑双面膜的患者外轮廓搜索条件，本研究建议平滑度为1，HU阈值为-550 HU。

Effects of Body search strategy on dosimetric calculations for PTV and OAR in radiotherapy

Abstract: Objective To analyze the effects of the volume differences introduced by the parameter setting of automatic Body search strategy on the dosimetric calculations for planning target volume (PTV) and organs-at-risk in patients immobilization with double-sided mask. Methods Twenty-five patients immobilized with double-sided mask for whole-brain radiotherapy were enrolled in the study. Keeping the other parameters unchanged, the Body search conditions (smoothing level, CT value threshold and post-processing method) were changed for dose calculation. A total of 9 treatment schemes were designed. The dosimetric differences in PTV and organs-at-risk between parameter-changed plans and Default plan were analyzed. Results The smoothing level and CT values had significant effects on the dosimetric parameters of Body and PTV. In DSL0, DSL1, DSL2, HU-550 and HU-750 plans, the Dmean of PTV and the Dmax of Body was changed obviously. The average change in Body Dmean exceeded 400 cGy in HU-750 plan. Conclusion The default Body search strategy in the Eclipse treatment planning system is not suitable for all situations. The Body search under low smoothness and low HU has a great effect on dose calculation. For the patient immobilized with double-sided mask for whole-brain radiotherapy, the recommended smoothness level and HU threshold are 1 and -550 HU, respectively.